1. Field of the Invention
The present invention relates to an X-ray focusing device for used in X-ray monitors in outer space, or radiation counters or microanalyzers on the ground.
2. Description of the Background Art
Differently from visible light, a normal-incidence optics is difficult to use for X-rays. Therefore, a grazing-incidence optics utilizing total reflection from a metal surface based on a property of metals, i.e. a refractive index less than one for X-rays, is used for X-rays. In view of the fact that a critical angle for the total reflection of X-rays has a small value of about 1 degree, the grazing-incidence optics has to be designed to ensure a sufficient effective area of a reflecting surface. In this context, there has been known a technique of concentrically arranging a plurality of metal cylindrical-shaped reflecting mirrors different in diameter. This technique, however, leads to a problem; namely an increase in total weight of an obtained X-ray reflecting device, which makes it difficult to transport the device from the ground for use in outer space.
Further, each reflecting mirror in the X-ray reflecting device can have a certain level of reflectance only if its surface has smoothness to the degree of an X-ray wavelength. For this purpose, the conventional X-ray reflecting device has been prepared by subjecting each reflecting surface to a polishing process, so as to ensure a desired surface smoothness. As a measure to ensure the desired smoothness, there has been developed a technique of preparing a numbers of replica mirrors by pressing a thin film onto a polished master block (see “X-ray Imaging Optics, T. Namioka, K. Yamashita, BAIFUKAN Co., Ltd.”: Non-Patent Document 1). In either case, a number of reflecting mirrors have to be prepared one by one by spending a lot of time and effort.
With the aim of achieving a reduction in weight, an X-ray reflecting device using silicon pore optics has also been proposed (see “Beijersbergen et al., (2004) Proc. SPIE Vol. 5488, pp. 868-874”: Non-Patent Document 6). This device comprises a plurality of polished silicon substrates each having a front surface serving as a reflecting mirror and a back surface formed with a groove for ensuring an X-ray optical path, wherein the adjacent silicon substrates are arranged in close contact with one another. However, this reflecting device is limited in weight reduction achieved, because the thickness (usually referred to as “P”) of walls which define slits (which corresponds to slits 121, 122, . . ., 12n in the undermentioned FIG. 1) is determined by a thickness (200 to 500 μm) of each of the silicon substrates. Moreover, the polished mirrors take a lot of time and effort to be prepared, as with the above metal-based device.
While an optics using a glass fiber as an X-ray waveguide has recently come into practical use (see, for example, “Kumakov & Sharov (1992) Nature 357, 390”: Non-Patent Document 2), it involves a problem about an increase in cost.